Triphenylcarbinol Derivatives as Molecules for Second-Order Nonlinear Optics

A series of novel tris D-pi-A substituted triphenylcarbinol derivatives have been synthesized and studied for their molecular second-order nonlinear optical properties by electric field induced second harmonic generation (EFISH) and hyper Rayleigh scattering (HRS). Compared to their phenyl analogs with only one D-pi-A system, the triphenylcarbinol derivatives 7 and 10-12 exhibit an increased hyperpolarizability ([beta] HRS) without the undesired red-shift of the charge-transfer band. The dipole moments and the hyperpolarizabilities are dependent on both the close proximity (3-4 angstrom) and the orientation of the three NLO-phore units. The nature of the acceptor substituent strongly influences the magnitude of the [beta]HRS values. The tris(nitrophenyl) derivative 7 exhibits a [beta]HRS value of 15 X 10(-31) esu, which is almost the same as that of its reference compound p-nitroanisole 13, whereas the tris(nitrostilbene) derivative 12 exhibits a [beta]HRs value of 338 x 10(-30) esu which is more than 3 times larger than that of its reference compound 4-methoxy-4'-nitrostilbene 16.